[R-390] A hard one ?

[Pete Williams]

​Why  do  I  get the  hard ones?  this is  a new  arrival.


IF  MODULE....It  goes into   oscillation..
1.. all  AGC  caps   changed
2... tubes   changed
3..  little or  no - AGC.    Can  also  see  + V on  AGC     (  about + 3
V)  depending on setting  of   RF  gain  and    local  audio..  AGC
terminals    correct R  to  chassis.
4.. Varying   local gain  and  RF  changes  character  of   oscillation as
heard  on   speaker.
 Testing  done  in  chassis  and    external on  extension  cable
5..   The  if  of   455 kHz  introduced  to  J513  from  sig, gen  and
output  level  varied      .Carrier  meter   works  but  has  gone
backwards  when AGC  goes   positive .
6...  tube potentials  to  be  checked  but   a   day of   audio
racket     a wonder  to  behold .


Do  I have a problem  ?

Cheers
Pete  Vk3IZ